This invention relates to an anode depletion detector particularly useful for hot water heater tanks.
Conventional gas or electric model hot water heaters do not have adequate mechanisms to monitor anodic protection devices for the glass coated, steel water tank. That is, the main body of a water heater is typically a steel vessel with a protective glass coating on the inside. Although the glass coating is nearly complete in its coverage of the inside surface of the tank, minute uncovered areas generally exist. These areas require protection against corrosion caused by hydrolysis.
It is known that a sacrificial anode installed within such a tank sufficiently protects the steel body by virtue of the galvanic reaction of the anode. Metals suitable as anode materials include aluminum, magnesium, zinc and zinc alloys. All of these metals rank higher in the ionization scale than steel.
When an anode material is present within the vessel of a water heater, the metal forms a positive pole or anode. The steel tank forms a negative pole or cathode. The constant flow of electric current from the positive anode metal to the steel body insures that the body will remain chemically inactive.
In such a system the direct current potential near the surface of a steel body must be at least 0.78 volts or greater. In practice, by use of the anode materials referenced above, the potential is maintained in the range of 1 to 1.5 volts so that a clearly sufficient tank protection is provided.
While the steel vessel is protected, the anode material is electrolytically consumed and transformed into oxides and hydroxides which settle at the bottom of the tank in a form of scale or are discharged with hot water. Finally, the anode material is totally depleted. When this happens the water heater tank is no longer protected and rust corrosion starts. Soon thereafter the tank may fail. When a tank is about to fail there is no prior indication. Rather the tank fails catastrophically, often causing total loss of hot water supply and water damage.
To avoid this experience, monitoring of the condition of a water heater is a desirable feature. In particular, it is desirable to monitor the condition of the anode material. This can be done by removing the anode material, which usually comprises a rod, from the water tank and making a visual inspection. Alternatively, a regular schedule for replacement of the anode material may be established. These procedures are, however, not easy. A special large socket wrench is normally required to unscrew the anode from a tank. The anode is normally not readily accessible. For example, head room to remove the anode is often not sufficient. All of these factors make it difficult to monitor the condition of an anode. For these reasons, such monitoring is normally ignored.
Therefore, a way to monitor the viability of an anode within a hot water heater tank in a convenient, simple and inexpensive manner has long been sought. The present invention constitutes a device which accomplishes this objective.